Enjo kōsai

Enjo kōsai is school girls going on dates with older guys for monetary benefits. Commonly thought of as amateur prostitution though in most cases no sexual activity is involved. They just do it as an easy way of making money. In the live action drama Great Teacher Onizuka Miyabi, pictured above, convinces her friends to go on paid dates for cash.

This does show up in Ranma ½ to varying degrees. Nabiki Tendo accepts date offers and invitations from classmates whom she then fleeces for all they're worth during the date. When she gets bored of being with them she proceeds to blackmail them with their own love letters to her.

The other character that does this is Ranma himself. Unlike Nabiki, Ranma is not really interested in money but he/she has went on dates to be compensated in someway for example his date with Shampoo to get the memory restoring shampoo or another date with her to get a potential cure for his curse.

More on this can be found at:
http://www.dawncenter.or.jp/english/publication/edawn/9911/mean.html